module ActiveSupport::Concern

Buzz.bar # => private method 'bar' called for Buzz:Class(NoMethodError)
Buzz.foo # => "foo"

end
include Example
class Buzz

end
end
def bar; puts 'bar'; end
private

def foo; puts 'foo'; end
class_methods do

extend ActiveSupport::Concern
module Example

You can define private class methods as well.
Define class methods from given block.

def class_methods(&class_methods_module_definition)
  mod = const_defined?(:ClassMethods, false) ?
    const_get(:ClassMethods) :
    const_set(:ClassMethods, Module.new)
  mod.module_eval(&class_methods_module_definition)
end